//This shows the relative length of the down trend.

//+------------------------------------------------------------------+
//|                                             RelDownTrLen_....mq4 |
//|                                                   Author: Martes |
//|               http://championship.mql4.com/2007/ru/users/Martes/ |
//+------------------------------------------------------------------+
#property copyright "Martes"
#property link      "http://championship.mql4.com/2007/ru/users/Martes/"

//Fix minimum (0) and maximum (1) levels manually. Levels below do not work.
#property indicator_maximum 1
#property indicator_minimum 0
//---
#property indicator_level1 0
#property indicator_level2 1
#property indicator_levelcolor clrLimeGreen
#property indicator_levelwidth 2
#property indicator_levelstyle STYLE_SOLID

#property indicator_separate_window

#property indicator_buffers 1
#property indicator_color1 clrMidnightBlue
#property indicator_width1 2

extern int barsToProcess=100;
extern int StartingBarNumber=0;
extern bool DrawForCandleBodies=true;

//---- buffers
double ExtMapBuffer1[];
//----
datetime ProcessedTime=0;
//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int init()
  {
//---- indicators
   SetIndexStyle(0,DRAW_LINE);
   SetIndexBuffer(0,ExtMapBuffer1);
//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator deinitialization function                       |
//+------------------------------------------------------------------+
int deinit()
  {
//----

//----
   return(0);
  }
//+------------------------------------------------------------------+
//| Custom indicator iteration function                              |
//+------------------------------------------------------------------+
int start()
  {
   int    counted_bars=IndicatorCounted();
//--- Variables for finding best down-trend
   int Length,StartIdx,EndIdx,
   BestLength=0,BestStartIdx=0,BestEndIdx=0;
   datetime BestStartTime,BestEndTime;
   double BestStartPrice,BestEndPrice;

//--- Do nothing if the current candle is already processed.
   if(ProcessedTime==Time[StartingBarNumber])
     {
      return(0);
     }
   else //Process
     {
      ProcessedTime=Time[StartingBarNumber];
      if(barsToProcess<=2)
        {
         if(barsToProcess<=1)
           {
            Print("Too few bars to calculate a down-trend");
            return(0);
           }
         else
           {
            if(DrawForCandleBodies)
              {
               BestStartPrice=CandleBodyMaximum(StartingBarNumber+2);
               BestEndPrice=CandleBodyMaximum(StartingBarNumber+1);
              }
            else
              {
               BestStartPrice=High[StartingBarNumber+2];
               BestEndPrice=High[StartingBarNumber+1];
              }
            if(BestStartPrice<=BestEndPrice)
              {
               ExtMapBuffer1[0]=0;
               Print("No down trend");
               return(0);
              }
            BestStartTime=Time[StartingBarNumber+2];
            BestEndTime=Time[StartingBarNumber+1];
           }
        }
      else //Find a Down-Trend with a convex hull.
        {
         ProcessedTime=Time[StartingBarNumber];
         int NumbersOfConvexHullVertices[],//To store indices (numbers) of Vertices in Convex Hull
         ConvexHullIdx,//This points to the last valid element of NumbersOfConvexHullVertices
         i;
         ArrayResize(NumbersOfConvexHullVertices,barsToProcess);

         double CandleBodyMaxima[],
         x0,y0,
         x1,y1,
         x2,y2;
         ArrayResize(CandleBodyMaxima,barsToProcess);
         //Fill array CandleBodyMaxima[] with values from 
         //the range StartingBarNumber+1 ... StartingBarNumber+barsToProcess of the chart
         for(i=1; i<=barsToProcess; i++)
           {
            if(DrawForCandleBodies)
              {
               CandleBodyMaxima[i-1]=CandleBodyMaximum(StartingBarNumber+i);
              }
            else
              {
               CandleBodyMaxima[i-1]=High[StartingBarNumber+i];
              }
           }
         //Find the lower part of the convex hull for points (i, CandleBodyMaxima[i]) of
         //the plane
         NumbersOfConvexHullVertices[0]=0;//This is the index of CandleBodyMaxima[0]
         ConvexHullIdx=0;//This says that NumbersOfConvexHullVertices[ConvexHullIdx] is valid.
         NumbersOfConvexHullVertices[1]=1;//This is the index of CandleBodyMaxima[1]
         ConvexHullIdx=1;//NumbersOfConvexHullVertices[ConvexHullIdx] is still thought to be valid.
         for(i=2; i<barsToProcess; i++)
           {
            ConvexHullIdx++;
            NumbersOfConvexHullVertices[ConvexHullIdx]=i;//The new point is added in the hull.
                                                         //Now we will make the hull convex
            x0=NumbersOfConvexHullVertices[ConvexHullIdx-2];
            y0=CandleBodyMaxima[NumbersOfConvexHullVertices[ConvexHullIdx-2]];
            x1=NumbersOfConvexHullVertices[ConvexHullIdx-1];
            y1=CandleBodyMaxima[NumbersOfConvexHullVertices[ConvexHullIdx-1]];
            x2=NumbersOfConvexHullVertices[ConvexHullIdx];
            y2=CandleBodyMaxima[NumbersOfConvexHullVertices[ConvexHullIdx]];
            while((isLeft(x0,y0,x1,y1,x2,y2)>=0) && (ConvexHullIdx>=2))
              {
               NumbersOfConvexHullVertices[ConvexHullIdx-1]=NumbersOfConvexHullVertices[ConvexHullIdx];
               ConvexHullIdx--;
               if(ConvexHullIdx>=2)//Enough points in the hull to process.
                 {
                  x0=NumbersOfConvexHullVertices[ConvexHullIdx-2];
                  y0=CandleBodyMaxima[NumbersOfConvexHullVertices[ConvexHullIdx-2]];
                  x1=NumbersOfConvexHullVertices[ConvexHullIdx-1];
                  y1=CandleBodyMaxima[NumbersOfConvexHullVertices[ConvexHullIdx-1]];
                  x2=NumbersOfConvexHullVertices[ConvexHullIdx];
                  y2=CandleBodyMaxima[NumbersOfConvexHullVertices[ConvexHullIdx]];
                 }//if
              }//while
           }//for
         //Find the longest down-trend
         for(i=0; i<ConvexHullIdx; i++)
           {
            StartIdx=NumbersOfConvexHullVertices[i];
            EndIdx=NumbersOfConvexHullVertices[i+1];
            Length=EndIdx-StartIdx;
            if(Length>BestLength && 
               CandleBodyMaxima[StartIdx]<CandleBodyMaxima[EndIdx])
              {
               BestStartIdx=StartIdx;
               BestEndIdx=EndIdx;
               BestLength=Length;
              }//if
           }//for
         if(BestLength==0)
           {
            ExtMapBuffer1[0]=0;
            Print("No down trend");
            return(0);
           }
         BestStartTime=Time[BestEndIdx+StartingBarNumber+1];
         BestEndTime=Time[BestStartIdx+StartingBarNumber+1];
         BestStartPrice=CandleBodyMaxima[BestEndIdx];
         BestEndPrice=CandleBodyMaxima[BestStartIdx];
        }//else //Find an Up-Trend with a convex hull.

      ExtMapBuffer1[0]=(1.0*BestLength)/barsToProcess;
      // Вариант: ExtMapBuffer1[0]=BestEndIdx/barsToProcess;

     }//else Process

//----
   return(0);
  }
//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
double CandleBodyMinimum(int CandleNumber)
  {
   return(MathMin(Open[CandleNumber], Close[CandleNumber]));
  }
//+------------------------------------------------------------------+
//|                                                                  |
//+------------------------------------------------------------------+
double CandleBodyMaximum(int CandleNumber)
  {
   return(MathMax(Open[CandleNumber], Close[CandleNumber]));
  }
//+------------------------------------------------------------------+
//| isLeft(): tests if a point is Left|On|Right of an infinite line. |
//|    Input:  three points P0=(x0,y0), P1=(x1,y1), and P2=(x2,y2).  |
//|    Return: >0 for P2 left of the line through P0 and P1          |
//|           =0 for P2 on the line                                  |
//|           <0 for P2 right of the line                            |
//+------------------------------------------------------------------+
double isLeft(double x0,double y0,double x1,double y1,double x2,double y2)
  {
   return( (x1-x0)*(y2-y0) - (x2-x0)*(y1-y0) );
  }
//+------------------------------------------------------------------+